This application is the national phase application under 35 U.S.C. xc2xa7371 of prior PCT International Application No. PCT/EP01/01980, which was published on Sep. 13, 2001 in the German language.
The present invention relates to a method and an apparatus for transversely gluing veneer strips to obtain a butt-glued veneer carpet.
It is known from the prior art that veneer strips are glued on their butt edges to produce a large veneer carpet.
To this end so-called transverse assembly machines for the butt gluing of wooden veneers are known from the prior art. In these machines, pre-glued veneer strips are transferred into a heating zone and are there glued together on their edges under the action of pressure and heat. It goes without saying that the joining areas of the veneer strips must each be oriented such that they are positioned in the heating zone.
An exact alignment of the rear edge of the respectively preceding veneer strip is achieved in the known apparatuses in that the veneer strip is transported beyond the heating zone and then subjected to a reversing counter-movement. Prior to the beginning of this counter-movement, stop pins against which the veneer strip is mechanically placed are extended in the area of the heating zone. The respectively next veneer strip to be glued is supplied in the meantime and also oriented relative to stop pins. Subsequently, the further veneer strip is moved against the stop pins still positioned in the heating zone and is thus aligned accordingly. For gluing the two veneer strips the heating zone is then closed, the stop pins are retracted. The preceding veneer strip is retained while the new additional veneer strip is pushed against the edge of the preceding veneer strip and held under tension until the joining process has been completed.
A drawback of this method is on the one hand that a lot of time is needed because of the reversing movement of the preceding strip. Furthermore, in the case of corrugated or warped veneer strips there is the risk that these are not exactly placed against the stop pins. Thus the veneer strips would not lie in planar fashion in front of the pins, but would have folds and other deformations. This also applies to the new veneer strip which is pushed against the edge of the preceding veneer strip after removal of the stop pins. There is again the risk that this displacement operation is not carried out exactly.
A similar method in which a veneer strip is aligned by means of pendulum type stops and first-sheet stops are described in Utility Model 93 01 196.2. The stops used in this case have the above-described drawbacks.
It is a further known from the prior art to pass on the resulting veneer carpet by one veneer strip width each after the joining operation and to fix it. There is the risk that tolerances in the veneer strip widths and the transportation mechanism add up with an increasing number of joints to such a degree that the edge of the veneer strip to be glued is no longer positioned in the area of the heating zone.
It is object of the present invention to provide a method and an apparatus of the above-mentioned type which permit a substantially automatic butt type gluing of veneer strips while being of a simple design and easily usable in an operationally reliable manner.
According to the invention this object is achieved by the two independent claims; the corresponding subclaims show further advantageous developments of the invention.
As far as the method is concerned, it is thus intended according to the invention that a first veneer strip is first transported or supplied, that the passage of the rear edge of the veneer strip is determined by means of a first sensor unit, that in response to the values determined by the first sensor unit, the transportation path needed up to a desired position of the rear edge of the veneer strip in the area of the heating zone is calculated, and that at least one transportation means is controlled or adjusted on the basis of the values determined.
The method according to the invention is characterized by a number of considerable advantages. First of all, it is possible according to the invention to entirely dispense with mechanical stop means, at least in the area of the heating zone. Thus, this fully excludes the risk that the edge of a veneer strip is not adequately or correctly placed against stop means. In addition, the mechanical construction of the apparatus is simplified because the mechanical stops means and their drive and control can be entirely dispensed with.
Thanks to the possibility provided according to the invention for controlling at least one transportation means, i.e. in the presence of several transportation means these means are controlled independently of each other, it is possible to align the veneer strip very exactly also in cases where the strip has an obliquely positioned edge or where the veneer strip is distorted or warped. Hence, according to the invention it is possible to position a veneer strip exactly and optionally to straighten the same and to simultaneously align the strip in parallel with the heating zone and to position the same therein. A reversing movement can here be dispensed with.
Hence, the method according to the invention can be employed for aligning the rear edge of a first veneer strip and also the respective front edges of the subsequent veneer strips. It is thus possible to carry out an optimized and perfect joining operation, independent of the number of veneer strips and of slight dimensional deviations.
In a particularly advantageous development of the invention, the position of the edge of the veneer strip is determined in a direction transverse to the direction of transportation by means of the first sensor means at a plurality of measuring points. Depending on the precision desired for the gluing operation, a sufficiently great number of measuring points can be used.
To ensure an exact alignment of edges of veneer strips that are not positioned at an exactly right angle relative to the transportation direction, it is particularly advantageous when the transportation takes place via several transportation means which are arranged side by side in the direction of transportation.
To avoid errors that might occur after passage through the first sensor unit, it is particularly advantageous to determine the position of the edge of the veneer strip by means of a second sensor unit in the area of the heating zone and to correct the position of the veneer strip, if necessary. It is thus possible to check once again within the heating zone whether the edge of the veneer strip is exactly positioned and to perform a correction, if necessary.
To achieve a uniform configuration of the veneer carpet for ensuring a high-quality precise joining operation, it is of particular advantage when the edge of the veneer strip is positioned in parallel with the heating zone arranged at a right angle relative to the direction of transportation. Thus, the joining area is always in optimum alignment with the heating zone.
In particular in the case of long or large veneer strips, there is the risk that these are warped or distorted. To compensate for such flaws, it is intended according to the invention that a distortion of the veneer strip is determined by means of the first and/or second sensor unit and that the plurality of transportation means are operated separately for a straight alignment of the veneer strip. It may here be of particular advantage when individual portions of the veneer strip are clamped for a straight alignment thereof. Other portions may be moved on by means of the transportation means, resulting in a straight joining edge.
It is of particular advantage when the veneer strip is reversingly movable in the direction of transportation behind the heating zone. For instance, it is in particular possible in the case of a first veneer strip to align the same in an optimum way in the heating zone after passage of its rear edge.
As far as the apparatus is concerned, the object underlying the invention is achieved by the following features: a first group of transportation means for supplying veneer strips, a first sensor unit in the area of the first group of transportation means, a heating zone arranged in a direction transverse to the direction of transportation, a second sensor unit in the area of the heating zone, a second group of transportation means arranged downstream of the heating zone, and a control and/or adjustment unit.
The apparatus according to the invention is also characterized by a number of considerable advantages. First of all, the whole structure of the apparatus is relatively simple because the stop elements, which are retractable into the plane of the veneer strips according to the prior art, can be entirely dispensed with. A soiling of or damage to the stop elements and the drives thereof is thus no longer possible. The manufacture of the apparatus is thereby simplified. In addition, the maintenance work is considerably reduced.
To be able to align the individual veneer strips in an exactly straight orientation relative to the heating zone and to be able to perform rotational movements as well, it is of particular advantage when the first group of transportation means comprises a plurality of separately operable transportation belts which are arranged side by side in the direction of transportation. This applies to the second group of transportation means as well.
The first and/or second group or transportation means has preferably assigned thereto counter-pressure means for contacting the surface of the veneer strips. It is possible with the help of these counter-pressure means to clamp the veneer strips in individual areas for compensating for distortions. The counter-pressure means preferably comprise bail elements which only effect a clamping at points and thus permit a rotation of the veneer strip.
According to the invention the first and second sensor units preferably comprise optical sensors. It is of particular advantage when several optical sensors are arranged in a row in a direction transverse to the direction of transportation. In an advantageous embodiment of the invention, the optical sensors thus form vertical light barriers. The passage of a front edge or a rear edge of a veneer strip can thus be detected and recorded very accurately. Since several light barriers of such a type are provided in a direction transverse to the direction of transportation, it is possible in a particularly reliable manner to detect the veneer strip exactly with respect to its original position and then to align the same.
The first and/or second group of transportation means is designed in a particularly advantageous manner such that it is operable both in the direction of transportation and also opposite to said direction of transportation.
The heating zone advantageously comprises upper and lower pressure elements to hold the veneer strips exactly during the joining operation.